Exemplary embodiments of the present invention relate generally to point-of-care screening tests of body fluids such as saliva, blood, and other fluids for analytes including drugs of abuse and other compounds and materials. More specifically, exemplary embodiments relate screening tests for body fluids that require a test sample to be treated and incubated for a desired period of time prior to being introduced to an immunoassay test strip.
The increased availability and use of drugs of abuse along with the need for testing of other analytical targets (“analytes”), for example HIV or antibodies thereto, has caused employers, governmental agencies, sports groups, hospital emergency rooms, and other organizations to utilize drug and analyte screening methods in a wide variety of situations such as in screening individuals for potential employment or purchasing insurance, or to maintain safety in the work place. Screening tests for the detection of drugs of abuse and other analytes range in complexity from very complex analytical procedures to simple immunoassay tests. For example, while simple, preliminary drug screening tests are typically performed for the purpose of quickly identifying on a qualitative basis, the presence of drugs in a body fluid such as urine or saliva, a complete analysis of the sample may then be carried out in a laboratory if the preliminary screening results are positive.
More and more such drug screenings are taking place on site, for example at the workplace or during routine police stops or check points. Thus, in settings such as law enforcement, there is a constant need for providing improved on-the-spot testing for drugs of abuse or other analytes in a quick and simple manner since initial tests will be far removed from the clinical setting. Such on-the-spot testing is facilitated through the use of point-of-care (POC) testing devices. The term “POC” encompasses many possible end-use settings outside of a centralized testing facility, ranging from regional health clinics and physicians' offices to emergency settings and other resource limited settings such at-home or mobile use. Such testing devices are designed accept a sample with relatively little or no pre-preparation, test for one or more analytical targets, and provide a result, which can be interpreted in a simple manner to provide the “answer”, in seconds to hours. The analytes of such tests can include proteins, nucleic acids, metabolites, drugs, dissolved ions and gases, human cells, and microbes. Samples may include blood, saliva, urine, or other bodily fluids or (semi)solids.
Thus, POC testing devices can provide results rapidly, where needed, as samples do not travel to a laboratory to await the attention of a skilled technician. Results do not wait to be transmitted and collected; rather, the user initiates the test and receives the results on the spot. Inevitably this saves time, but as these tests are typically carried out by testing personnel who are generally not technically trained as would be a laboratory technician, the lack of professional control and the potential for incorrect interpretation of results leads to concerns that accuracy or reliability are being traded for speed. It is thus important that the drug screening procedure be simple yet reliable and that the testing apparatus be designed so as to enable the testing personnel to avoid all contact with the fluid specimen which is being tested.
Over the years the speed and specificity of immunoassays have made them one of the most accepted methods for screening for drugs of abuse in body fluids. Immunoassay is accomplished in minutes to an hour or more (depending on incubation times). A major class of immunoassay POC testing is the lateral flow test, which uses a membrane or paper strip to indicate the presence of protein markers such as pathogen antigens or host antibodies. On a membrane, addition of sample induces capillary action without user intervention (leveraging capillary forces for fluid actuation). As the sample flows across the membrane, it gathers labeling reagents embedded in the membrane, and flows over an area that contains capture molecules; the labeled captured analytes are interpreted by eye to form a visible band. In the U.S., lateral flow tests are most notably used for pregnancy testing, screening for infectious diseases and drugs of abuse, and for measurement of protein markers in blood to aid rapid clinical diagnostics of life-threatening events such as heart attack, stroke, and deep-vein thrombosis. In developing countries, the lateral flow test is widely used to diagnose HIV.
The large investment in lateral flow devices has resulted in significant interest in trying to improve their performance in producing highly reproducible, quantitative, and sensitive results. Although the test may be simple to perform using a lateral flow device, difficulties of measurement can arise because the unit operations (particularly mixing, incubation timing, sample normalization, and rinsing) may not be as well controlled as in a laboratory machine. Efforts to address the critical issues of error and accuracy have targeted control of the sample volume into which the label is dispersed, uniformity of dispersion, and flow rate, which is the main determinant of contact and incubation times.
While blood and urine samples have long been the primary fluids used for testing for disease as well as for evidence of substance abuse, there is increasing interest in testing regimens which can test a variety of body fluids including salivary specimens. Some advantages in a system that can test saliva in addition to bodily fluids more traditionally used in testing are that it is relatively easy to obtain a saliva sample and that a saliva sample obtained on the spot cannot be adulterated. Also, saliva testing is more suitable in testing of recent use since it does not maintain reactivity of the analyte after use for up to four to six weeks. Accordingly, testing of saliva gives a result in real time within a span of hours as compared to urine which gives a test result after-the-fact. In general, saliva and blood are useful to measure impairment, while urine tests generally are not suitable for this purpose.
Nevertheless, the ability to collect and analyze saliva samples in addition to other bodily fluids using an immunoassay for diagnostic purposes is complicated by the relatively high viscosity of the fluid and the small volumes of salivary fluid secreted. In particular, saliva contains mucins, which are a family of large, heavily glycosylated proteins that account for many of the properties of saliva. These mucins also act to disrupt or inhibit the lateral flow necessary to achieve a rapid and accurate test result and considerably restrict the time it takes for a sample to travel through the immunoassay strip as well as the amount of the target compound in the sample which can travel up the strip and thus be measured by the immunoassay.
Because of the problems caused by mucins, certain testing systems have recommended long and elaborate procedures for removing mucins prior to testing the sample. These procedures include pre-treating a sample such as saliva with a diluent or other reagent which is capable of breaking down the interferants in a sample, e.g., mucins in saliva, so that these interferants do not restrict the capillary flow of the sample through the test strip, in order to try to achieve a rapid test of target compounds. However, these pre-treatment steps with specific reagents to dilute or denature interferants, modify analyte structure, or release analyte from binders must generally be performed outside the confines of the test device. This requires persons administering the test to take additional steps and handle additional solutions. For example, it is necessary to suitably collect the sample, have the sample expressed into a buffer solution, and then have the expressed sample dispensed into a reaction well, which typically contains a second reagent such as an identifying reagent, all prior to introducing the testing solution including the sample onto an immunoassay test strip. All these steps necessitate the development of means and techniques for constructing self-contained devices which can test for saliva in addition to other body fluids in a manner that allows one to safely and efficiently control the test sample during pre-treatment and testing while remaining simple to use and providing the ability to obtain accurate results.